Comparing pretreatment methods for improving microalgae anaerobic digestion: Thermal, hydrothermal, microwave and ultrasound

Abstract

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Cell disruption technologies

“…Ultrasound microalgae pretreatment has been mainly applied for biodiesel, bioethanol, and biogas production and has been proven to adequately break algal cells in low concentration biomass suspension. Passos et al (2015a) reported that ultrasound pretreatment (20 kHz, 30 min, 26.7 MJ/kg TS) increased the soluble fraction of organic matter, proteins, carbohydrates, and lipids 7-, 12-, 9-, and 3-fold compared to untreated samples. Likewise, Silva et al (2014) applied ultrasounds (40 kHz, 60 min) on a mixed microalgae culture composed of Chlorophyceae, Cyanophyceae, Euglenophyceae, and Bacillariophyceae, obtaining lipid extraction yields of 13.3%.…”

“…Apart from biomass concentration, pretreatment time and power of microwaves are the main operation parameters. Passos et al (2015a) used microwaves to increase the soluble fraction of organic matter, proteins, carbohydrates, and lipids by a factor of 8, 18, 12, and nearly 2, respectively, compared to the untreated biomass. Silva et al (2014) applied a microwave pretreatment (400 W, 4 min) on mixed culture biomass of Chlorophyceae, Cyanophyceae, Euglenophyceae, and Bacillariophyceae and reported a remarkably higher lipid extraction (33.7%) compared to the untreated sample (4.8%).…”

Effect of Different Mixed Microflora on the Performance of Thermophilic Microaerobic Pretreatment

“…When the air load was 12.5 mL/L R -d, cumulative methane yield reached maximum, which was 216.8 mL/g VS substrate and 16.5% higher than that of sample under anaerobic condition. Improved methane yield from cellulosic substrate after pretreatment has also been reported by other authors [24][25][26]. Though the improvements were different, (this has something to do with the composition of the substrate and the different operational conditions [24]) these methods all can accelerate the hydrolysis process by destroying the substrate Fig.…”

The application of microwave heating in bioenergy: A review on the microwave pre-treatment and upgrading technologies for biomass

“…AD offers an alternative option for converting microalgal biomass in its entirety (without the need for any prior drying for water removal and/or prior pre-treatment steps) into a final product of useable energy [171]. Nevertheless, due to the complex structure and composition of the microalgal cell wall which hinders the initial hydrolysis step, pre-treatment methodologies have also been applied to improve the ultimate methane production yields and the biodegradability of the biomass [172]. In the work of Passos et al [173], the specific energy (regardless of the output power and exposure time) of the MW pre-treatment on microalgae biomass cultivated in High Rate Algal Ponds (HRAP), played an important effect on biomass solubilisation and final methane yields.…”